Loss In Weight Blenders

Loss in weight
blenders, functioning in a target weight mode, have been used for film and sheet extrusion for over 35 years.
Designed for a combination of high accuracy metering and homogenous ingredient blending, they provide these
features at the higher processing rates typical of the extrusion process.

A typical target weight loss weight blender has each metering feeder mounted to an independent, load
cell supported, weighing hopper. In some designs, the metering feeder is separated (de-coupled) from the weighing
hopper to lessen the amount of "dead load" on the load cell. The purpose for this is to improve the resolution of
the live load being weighed. This can be important when small amounts of a material are required in a formulation.
However, de-coupling adds complexity to the system, is sensitive to poor material flow properties and can cause
errors in the blend proportions if the principles of operation are not properly understood and followed.

For these reasons, the majority of loss weight feeder stations supplied to the industry utilize a feeder coupled
to the weigh hopper. Each weigh hopper measures the weight of material leaving it. The weighing system is
programmed for simultaneous and proportional metering of each ingredient. Since each ingredient is weighed
using an independent load cell, each cell can be sized and spanned to maximize the resolution of the A/D
conversions. This yields very precise and accurate weightiness.

Although metering is done proportionally
and simultaneously, this type of blender is programmed with a target, proportional weight for each ingredient
with the proportional feed rates set and derived from the weigh proportions. The material that is fed out of
the weigh hoppers is delivered to an active mixer. The feeding is paused after the target weights are
achieved and the loss weight hoppers are refilled if necessary in preparation for the next gravimetric feed
cycle. Since, unlike target rate blenders discussed next, refilling of the weigh hoppers is done while the
feed cycle is paused, the feeders always run in gravimetric mode. All material fed is weighed. After the
metered materials are mixed, the mixer discharges to the process and the next weigh cycle is started.
Refilling of the weigh hoppers while the feed cycle is paused allows for self-loading vacuum weigh hoppers
on this type of blender. This feature can be a significant advantage where adequate headroom is not available
for separate weigh hoppers with vacuum receivers above.

Loss In Weight Blenders: Applications and Modes of Operation

The Foremost Loss Weigh Blender is a unique blender for bulk-dry solids, which uses feeders to automatically meter
materials, chosen by the user, into the user's process.

The blender is designed, standard, with three modes of operation. The Mode of operation that the blender is to run
in is chosen by the user. These modes are:

MAUNAL MODE: The operator has full control of the blender and can use specific buttons on the displays to run the system manually.

GRAVIMETRIC MODE: The blender runs automatically, using the scaling functions of the blender to deliver the proper WEIGHT of
each material, as set by the operator.

VOLUMETRIC MODE: The blender runs automatically to deliver the proper RATIO of each material into the process.

Since the Gravimetric Mode uses the load cells to accurately weigh the material, it is the normal and recommended
mode of operation. But, if the condition should ever arise, where the Gravimetric Mode is not functional, or practical,
the blender can still be used to get blended material to the process. An operator need only change the mode of operation
to the Volumetric Mode. The Volumetric Mode can also be used to purge the blender automatically.

Mechanical Features

Each Loss-Weight Blending System consists of the following standard components:

1. Two (2) to ten (10) combination vacuum/weigh hoppers. One for each component supplied complete with:

3. All of the above components are rigidly mounted on a leg assembly for floor mounting. Includes all limit switches,
scale components, compressed air connections and vacuum control valves for completely automatic operation. The vacuum control
valves will be mounted on a manifold on the blender.

4. One (1) Mixer to receive material from the collection chute:

Either a barrel or center type

low level switch

Either gravity dump or vacuum take away outlets

Optional Components:

Stainless steel construction

Powder chamber with compressed air filter cleaning for powder or dusty materials

Auger feeders in place of vibratory feeders

Flow inducers for hard to move materials

Material sampling/calibration chutes

Vacuum loader power units to load and unload

Vacuum Barrel mixers to be mounted above customer process equipment

Separate Vacuum and weigh hoppers for continuous operation

Control Features

Model FDP-VII-LWB, Automated Blender Control System. The system is complete with: